Cross-references to Related Applications
Copending patent application Ser. No. 07/996,699 filed Dec. 24, 1992, of Tsvika Kurts, entitled "TWISTED PAIR ETHERNET HUB FOR A STAR LOCAL AREA NETWORK" assigned to Intel Corporation, the assignee of the present invention.
1. Field of the Invention
The invention relates to data processing systems and more particularly to a method and apparatus for communicating among a plurality of local area networks that are connected together.
2. Description of the Related Art
A Local Area Network, or LAN, is a data communications system which allows a number of independent devices to communicate with each other within a moderately sized geographical area. The term LAN is used to describe networks in which most of the processing tasks are performed by a workstation such as a personal computer rather than by shared resources.
A LAN node consists of a desktop workstation which performs processing tasks and serves as the user's interface to the network. A wiring system connects the workstations together, and a software operating system handles the execution of tasks on the network.
The configuration of the various pieces of the network is referred to as the topology. In a star topology, such as that defined in the IEEE 802.3 10baseT network standard or the 100 Mbps ETHERNET local area network based on a star topology, the switching control is at the center of the network. All of the attached devices, the individual workstations, shared peripherals, and storage devices, are on individual links directly connected to the center of the star. In the star configuration, all of these devices communicate with each other through the center which receives signals and transmits them out to their appropriate destinations. In the above-referenced copending patent application Ser. No. 07/996,699 a hub is described for a star local area network. The hub increases the link throughput by providing a means for reducing the number of collisions and the collision penalty when collisions do occur. A plurality of stations are connected to a common hub. A selection logic selects a preferred station and a preferred station frame from among ones of the plurality of stations that attempt to transmit a frame simultaneously. The selection logic performs a precedence algorithm, the ones of the plurality of stations that attempt to transmit a frame that are not selected being designated as non-preferred stations. A preferred station frame (which includes a destination address) is transmitted from the preferred station to pass through the common hub to the plurality of stations. A decoder decodes the destination address of the selected frame to thereby identify a destination station of the preferred station. A collision detector detects a collision detect signal from the non-preferred stations that attempt to transmit a frame. A small FIFO (first-in first-out buffer) in the switching means stores the preferred station frame from the preferred station, upon the condition that the collision detection means detects a collision detect signal from the destination station.
It is desirable to be able to connect together two or more hubs of the type described above to increase the number of ports and thereby expand an existing network to accommodate more stations.
It is an object of the present invention to provide a method and means of connecting together two or more hubs to increase the number of ports.
It is a further object of the present invention to provide a multi-hub precedence algorithm that is distributed and is executed in parallel in all of the hubs, such that the performance penalty due to cascading the hubs is low.